1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copier, or a facsimile apparatus, and more particularly to attaching positions and attitudes of circuit boards in an image forming apparatus.
2. Description of the Related Art
JP-A-10-143053 and JP-A-11-341203 disclose an electrophotographic image forming apparatus such as a laser printer or a laser facsimile in which an image forming unit is disposed in an upper side of a body frame and a plurality of circuit boards (control boards) are placed horizontally in a lower face side of the body frame.
According to these related arts, as the number of circuit boards increases, the plan view area of the body frame must be enlarged to house the circuit boards. This causes an increase in size of the image forming apparatus.
JP-A-10-143053 and JP-A-11-341203 further disclose that a low voltage power board, a high voltage power board, and a main control board are placed horizontally in the lower part of a main frame and a space that is isolated from a sheet path space through which a printing medium passes is defined at the rear of the main frame for placing an NCU board in an upright state. The NCU board is placed so as to become, in a plan view, orthogonal to a drive system unit placed on one side of the main frame.
In these related arts, a laser scanner unit as an exposure unit is placed below a process unit as an image forming unit and thus a wiring between the boards and the laser scanner unit can be shortened. However, in the case where the laser scanner unit, the image forming unit, and the main control board are placed from above, a harness for connecting the main control board and the laser scanner unit lengthens and a high-frequency signal is sent to the harness. Thus, noise is easily produced from the harness and noise occurring from actuators of solenoids, motors, etc., is easily picked up by the harness. If noise is thus picked up, a formed image easily becomes irregular.
In the case where the main control board is positioned in the lower part of the main frame, the harness between the main control board and a key switch portion positioned in the upper part of the image forming apparatus lengthens. Further, in a complex image forming apparatus provided by adding a facsimile function and an original read scanner function to a printer, an original read section is generally placed on the top of the apparatus and thus the harness for transmitting a signal from a line CCD image pickup device (image sensor), etc., of the original read section to the main control board lengthens and electric noise easily gets mixed in at the middle of the harness.